Catheters are placed at various locations within a patient for a wide variety of purposes and medical procedures. For example only, one type of catheter is a balloon dilation catheter which is used in the treatment of a vascular stenosis. Such a catheter has a balloon at its distal end which is intended to be placed, in a deflated condition, within the stenosis, and then inflated while in the stenosis to expand radially the stenosed lumen of the blood vessel. Typically, the placement of such catheters involves the use of a guidewire which may be advanced through the patient's vasculature to the location which is to be treated. The catheter, which has a lumen adapted to receive the guidewire, then is advanced over the wire, or the wire and the catheter may be advanced in unison with the wire protruding from the distal end of the catheter. In either case, the wire serves to guide the catheter to the location to be treated.
It often becomes necessary, in the performance of a catheter procedure, to exchange the indwelling catheter for another catheter, for example, for a catheter having a different size balloon. In a typical catheter exchange, the guidewire first is removed from the lumen of the indwelling catheter. Then a longer exchange wire, usually about twice the length of the catheter, is passed through the catheter to replace the original wire. Then, while holding the exchange wire by its proximal end to maintain it in place, the catheter is withdrawn proximally from the blood vessel over the exchange wire. After the first catheter has been removed, the next catheter then is threaded onto the proximal end of the exchange wire and is advanced along the exchange wire and through the patient's blood vessels until the distal end of the catheter is located as desired. The exchange wire may be permitted to remain in place or may be exchanged for a shorter, conventional length guidewire.
A device, referred to as the "monorail" system, has been proposed recently which would modify the foregoing catheter exchange technique. In the proposed monorail system, the catheter is formed so that the guidewire is located outside of the catheter except for a short segment at the distal end of the catheter, which passes over the wire. The distal segment of the catheter has a short lumen which extends from the distal tip of the catheter to a more proximally located opening near the distal tip. In use, the guidewire is placed initially in the patient's vascular system. The distal segment of the catheter then is threaded onto the wire. The catheter can be advanced alongside the wire with its distal segment being attached to and guided along the wire. The catheter can be removed and exchanged for another catheter without the use of the usual double length exchange wire and without requiring withdrawal of the initially placed guidewire.
Although the proposed monorail catheter system may avoid the requirement for using a long exchange wire, it presents several difficulties. For example, it is not possible to exchange guidewires in an indwelling catheter, should that be desired. Additionally, the device presents a potential for damaging the delicate inner surface of an artery from a tension load applied to the guidewire which would tend to straighten the artery. Also, there is an increased risk of guidewire entanglement in those procedures where multiple guidewires are used, because the guidewires are exposed within the blood vessel. It is among the general objects of the invention to provide an improved device which overcomes the foregoing difficulties.